Process of manufacturing acetic anhydride



Patented July 26, i927.

u Eo STATJES PATENT OFFICE.

RUDOLF MEIITGAS'I AND MARTIN MUG-DAN, 'OF MUNICH, GERMANY, ASSIGNOBS TO CONSORTIUM F-UER ELEKTBOCHEMISCHE INDUSTRIE, OF MUNICH, GERMANY.

rnocnss or MANUFACTURING AOETIC mmznninn.

Ito-Drawing. Application filed February 21, 1925,8eria1 No. 10,953, and in Germany February 25, 1024.

In'our Patent 1,507,514 granted Jan. 19, 1926, a process of manufacturing acetic anhydride is described which consists in passing acetic acid vapor over a heated phosphate,- preferably a phosphate of the aluminium group. i i

According to this invention sodium phosphate, particularly one having a proportion of sodium to phosphorus less than 3Na to 1P, has an effect in splitting the acetic acid at least as good as that of metal-phosphates ,fl described in the above patent, and at the same time ofl'ers advantages not obtained when using other phosphates. Thus sodium phosphate is not only cheaperthan other phosphates but ma be recovered or purified by extraction wit water when unable to continue to act'as a catalyst.

It has been found, however, that sodium metaphosphate distributed on a material to which it is ind ifierent at a high temperature, such as graphite silicon, or silicon carbide, has an almost unlimited activity whereas when the'phosphate is", distributed on a silicate it sufiers in due course depreciation in activity owing to the fact that it attacks the silicatea The activity of sodium hosphate is especially ood when the phosp ate has been previous y heated to a temperature above 700 (3., for example from@8( )0900 C. It appears that at this.

high temperature salts of polymerized metaphosphoric acid'are formed which are more active than the ordinary sodium phosphate.

The following examples illustrate the invention, the parts being by weight:

. Example I. i

45 parts of carborundum of suitable sized grain are mixed with a solution of 14,9 parts'of' crystallized Na HPO ,12H O and 4,9 parts of ortho-phosphoric acid of 84 per cent strength in parts of water; the water is evaporated so that there is left carborundum coated with sodium phosphate, which is then heated for an hour at 900. The catalyst thus obtained is filled in a graphite 1 similarly to sodium phosphate.

or of an alkali metal phosphate with another phosphate the melting point of this mixture may be below the temperature at which the scissi0n of acetic acid occurs. In this case there is thefurther, advantage that a liquid can be used as-cata-lyst through which the vapor of acetic acid is conducted, with the result that the transmission of heat from the source of heat. to the zone of reaction is much improved, particularly when .stir ring is also adopted; the output from the apparatus is thereby increased. WVhen a liquid catalytic contact is used carbon or graphite containers have proved themselves good materials for the construction of the also be used. however, providedthey have.

suflicient resistance to chemical attack. The

coating of liquid alkali metal-phosphate v appears to prevent injultious action of the metal in the course of the reaction.

Example II.

As catalyst there is used a mass made by mixing 102' parts of Li CO 793 parts of Na HPO l2H O and 405 parts of H l-"O and heating the mixture at 850C. Through "this mass contained in a molten condition at 1. A process of manufacturing acetican- 1 1 hydride which comprises'passing acetic acid vapor in contact with an alkali metal phosphate heated to between 400 C. and 800 C.

2. A process of manufacturing acetic anhydride which comprises passing acetic acid vapor in contact with an alkali metal phosphate containin more than one atom of phos horns to "t rec atoms of alkali metal and eated to between 400 C, and 800 C.

' 3. A process of manufacturing acetic anhydride which comprises passing heatedivapors of acetic acid m contact with a molten alkali metal phos hate. 4. A process 0 manufacturing acetic an- 70 vessel and the stirrer. Metals or alloys may hydride which comprises passing acetic acid vapor at a temperature of 600 C. to 800 C. in contact with a melt containing an alkali metal phosphate. 1

5. A process of manufacturing acetic anhydride which comprises passing acetic acid vapor at Ya temperature of 600 C. to 800 C.

in contact with a melted mixture of alkali metal phosphates.

6. A process of manufacturing acetic in hydride which comprises passing acetic acid vapor at a temperature of 600 C. to 800 C. in contact with a melted mixture of alkali metal metaphosphates} v 7. A process of manufacturing acetic an- 15 hydride which comprises passing acetic acid vapor at a temperature of 600 C. to 800 C. in contact with a melted mixture of alkali metal phosphates in a graphite vssel.

RUDOLF, MEINGAST; MARTIN MUGDAN. 

